Madison police released a report Monday on the July 31 incident, without revealing the officer's name or gender. The department said the Taser accidentally discharged during a standard checkout procedure.

According to a summary of the investigation, officers are required to make sure no air cartridges are loaded before testing the Taser gun at the start of each shift. It's the air cartridges that propel the Taser's prongs, which deliver a jolt of electricity when they strike a target.

The officer's hand was injured, police spokesman Joel DeSpain said.

A letter of reprimand was issued because failing to ensure the air cartridge wasn't loaded was a violation of department policy, the report said.